(1) Field of the Invention
The present invention relates generally to valve assemblies, and more particularly to a disk valve assembly having a perforated bellows to reduce operational noise.
(2) Description of the Prior Art
Flow induced hydraulic valve noise can be attributed to the noise produced during the shifting of the valve (such as a disk valve) from the closed to the open position, the noise produced when the valve is fully opened, and the noise produced when the valve is closed. The noise generated during the opening and closing of a valve under pressure has often been identified as the greatest flow induced noise.
When a valve is opened, noise can be attributed to the sudden pressure rise downstream of a valve which results in three possible noise events. The first of these noise events is the pressure transient itself that impacts the piping and excites flexural vibration modes. The second is the possible cavitation of the fluid through the valve orifice, i.e., the high initial flow velocity through the orifice plate causes a pressure drop below the fluid vapor pressure. The third possible noise event is the high velocity turbulent flow through the valve that occurs when it is initially opened. The fluctuating pressures associated with the turbulent boundary layer can excite flexural vibrations of the piping.
When a valve is suddenly closed, the momentum of the fluid is absorbed by the expansion of the upstream piping. The sudden load will also transmit a pressure wave through the piping (known as water hammer) and possibly excite flexural modes of the piping. A second source of noise at closure is cavitation. Just downstream of the valve, cavitation can occur due to the sudden drop in static pressure from the momentum of the downstream fluid mass being rapidly retarded.